Effects of tillage systems on soil organic carbon dynamics, structural stablity and crop yields in irrigated wheat (Triticum aestivum L.)-cotton (Gossypium hirsutum L.) rotation in semi-arid Zimbabwe

Willis Gwenzi, J. Gotosa, S. Chakanetsa, Z. Mutema

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    Abstract

    Abstract In southern Africa, tillage research hasfocused on rainfed smallholder cropping systems,while literature on high-input irrigated croppingsystems is limited. We evaluated the effects ofconventional (CT), minimum (MT) and no-till (NT)tillage systems on soil organic carbon (SOC), bulkdensity, water-stable aggregates (WSA), meanweighted diameter (MWD) and crop yields in anirrigated wheat–cotton rotation. Soil data were monitoredin the first and final year, while yields weremonitored seasonally. Average bulk densities(1.5–1.7 Mg m-3) were similar among tillage systems,but often exceeded the critical limit (1.60 Mg m-3)for optimum root growth. Conversion from CT to MTand NT failed to ameliorate the high bulk densitiesassociated with the alluvial soil. SOC (g kg-1) at0–15 cm was higher (P\0.05) under MT (3.9–5.8)and NT (4.2–5.6) than CT (2.9–3.3). Correspondinghorizon SOC stocks (Mg C ha-1) for the tillagetreatments were; 9.3–13.9 (MT), 9.3–13.5 (NT) and7.3–7.7 (CT). In the final year, significant (P\0.05)tillage effects on SOC stocks were also observed at15–30 cm. Cumulative SOC stocks (Mg C ha-1) inthe 0–60 cm profile were higher (P\0.05) underMT (32.8–39.9) and NT (32.9–41.6) than CT(27.8–30.9). On average, MT and NT sequesteredbetween 0.55 and 0.78 Mg C ha-1 year-1 at 0–30 cmdepth, but a net decline (0.13 Mg C ha-1 year-1)was observed under CT. At 0–30 cm, MT and NThad higher (P\0.05) MWD (0.19–0.23 mm) andWSA (2.3–3.5%) than CT (MWD: 0.1–0.12 mm,WSA: &1.0%). Both MWD and WSA were significantly(P\0.05) correlated to SOC. Seasonal yieldsshowed significant (P\0.05) tillage effects, but6-year mean yields (t ha-1) were similar (CT: 4.49,MT: 4.33, NT: 4.32 for wheat; CT: 3.30, MT: 2.82,NT: 2.83 for cotton). Overall, MT and NT improvedsoil structural stability and carbon sequestration, while impacts on crop productivity were limited. Therefore,MT and NT are more sustainable tillage systems forthe semi-arid regions than conventional tillage.
    Original languageEnglish
    Pages (from-to)211-221
    JournalNutrient Cycling in Agroecosystems
    Volume83
    Issue number3
    DOIs
    Publication statusPublished - 2009

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